Synthesis and comparative η1-alkyl and sterically induced reduction reactivity of (C5Me5)3Ln complexes of La, Ce, Pr, Nd, and Sm

The synthesis of (C5Me5)(3)Ce and (C5Me5)(3)Pr from [(C5Me5)(2)Ln] [(mu-Ph)(2)BPh2] and KC5Me5 completes the series of sterically crowded (C5Me5)(3)Ln complexes for the larger lanthanides, La-Nd and Sm, and allows a comparison of structure and reactivity as a function of metal size. Synthesis of these new (C5Me5)(3)Ln complexes required silylated glassware, which surprisingly was not necessary for the more sterically crowded analogues. (C5Me5)(3)Ce and (C5Me5)(3)Pr display longer Ln-C(C5Me5) distances than any previously described Ce or Pr complexes containing the (C5Me5)(-) ligand. The eta(1)-C5Me5 alkyl-like reactivity of the (C5Me5)(3)Ln complexes was investigated with CO2 ethylene, THF, and H-2. The sterically induced reduction (SIR) reactivity of the (C5Me5)(3)Ln complexes was examined with Se=PPh3, AgBPh4, C8H8, and phenazine. All of these data indicate that (C5Me5)(3)Ln reactivity increases with decreasing size of the metal and hence increased steric crowding. The reactivity of (C5Me5)(3)Ln with CO2 and with Et3NHBPh4 was examined since each substrate could react by either eta(1)-C5Me5 alkyl or SIR pathways. In both cases, alkyl-like reactivity is observed: CO2 forms the insertion product (C5Me5)(2)Ln(O2CC5Me5), containing a carboxylate with a pentamethylcyclopentadiene substituent, and Et3NHBPh4 forms [(C5Me5)(2)Ln] [(mu-Ph)(2)BPh2] and C5Me5H. The reactions of (C5Me5)(3)Sm with aryl halides and primary alkyl halide radical clocks (RX) yield C5Me5R, C5Me5X, (C5Me5)(2), R-R, and [(C5Me5)(x)SmXy](z) as products, which indicate that SIR is not the only reaction pathway with these substrates. The X-ray crystal structures of the (C5Me5)(3)Ln reaction products [(C5Me5)(2)La](2)(mu-eta(2):eta(2)-Se-2), [(C5Me5)(2)(THF)La](2)(mu-eta(2):eta(2)-Se-2), [(C5Me5)(2)La](2)(mu-eta(3):eta(3)-Cl2N2H8), [(C5Me5)(2)Sm(mu-I)](3), and (C5Me5)(2)Sm(O2CC5Me5) are described as well as a new synthesis of (C5Me5)(3)Sm from (C5Me5)(2)Sm and (C5Me5)(2).